Fig. 1. Structure of the model. The incidence of HIV infection for calendar time t is represented by I(t). Immediately after infection, all individuals enter the primary stage of infection. After primary infection, the individual enters one of four AIDS-free CD4 compartments of undiagnosed HIV infection at the rate of fi qP. The sum of fi equals 1. In the absence of treatment, the individual will continue to the next compartment at a rate of qi (i = 1, 2). During each stage, except the primary infection stage, the individual can be diagnosed with HIV infection at a rate of di(t). This figure is a modified version of a figure of van Sighem et al.13.
HIV = human immunodeficiency virus, AIDS = acquired immune deficiency syndrome.